1. Field of the Invention
The present invention relates to an ultrasonic micro spectrometer for measuring and evaluating physical characteristics of a sample, measuring thickness of layers of laminated samples, and judging adhesion between layers of a sample, for example.
2. Description of the Related Art
The present inventors have previously disclosed an ultrasonic micro spectrometer in their earlier application, U.S. Ser. No. 07/495,961 (now U.S. Pat. No. 5,079,952) which incorporates a sensor composed of ultrasonic transducers making up transmitters and receivers in pairs capable of independently executing transmission and reception of ultrasonic waves. One of the ultrasonic transducers in the pair contains a recessed or concave transmission/reception surface, whereas the other ultrasonic transducer contains a planar transmission/reception surface. Either of the above-mentioned transducers may be provided for receiving or for transmitting waves. For explanatory purposes, an example of the operation of the above ultrasonic micro spectrometer is described below, wherein one of the ultrasonic transducers having a concave surface serves as a transmitter and the ultrasonic transducer having a planar surface serves as a receiver for example.
When the transmitter receives a wide-band high frequency voltage pulse, wide-band high-frequency ultrasonic waves are generated from the concave surface of the ultrasonic transducer. The wide-band high-frequency ultrasonic waves are transmitted onto the surface of a sample while being converged by the concave surface of the transmitter. Upon arrival at the surface of the sample, the converged ultrasonic waves scatter in a direction corresponding to an aperture angle of the concave surface of the transmitter before being reflected by the surface of the sample. The reflected waves are received by the planar receptive surface of the other ultrasonic transducer, serving as a receiver, in a wide variety of directions. The received waves are converted into electric signals corresponding to the intensity of the reflected waves before being delivered to a spectroanalyzer.
Next, based on the signal output from the receiver, the spectroanalyzer forms a distribution of the spectral intensity indicating the intensity of the reflected waves as a function of frequency. Response characteristics of a variety of frequency components can be analyzed by referring to the distribution of the spectral intensity. Based on the results of the analysis of response characteristics, the ultrasonic micro spectrometer evaluates the physical characteristics of the sample and measures the thickness of laminated layers of the sample.
When the reflected waves are converted into electric signals by the receiver, since the receiver has a planar receptive surface, those reflective waves containing components capable of orthogonally intersecting the planar surface are effectively converted into electric signals. On the other hand, those reflective waves containing other, non-orthogonal components cannot fully be converted into electric signals. Because of this, the reflective waves which are converted by the receiver are extremely dependent on the physical characteristics of the sample when receiving ultrasonic waves at a specific angle of incidence.
As a result, when scanning the transmitted waves along the surface of the objective sample, variation of the spectral intensity of the reflected waves can precisely be detected in each measuring position. The spectral intensity is further varied based on the elastic characteristics and surface condition of the sample.
Nevertheless, when dealing with a sample containing certain characteristics which may prevent the intensity of reflected waves from being dependent on the frequency or the angle of incidence of the ultrasonic waves, no variation occurs at all in the intensity of the reflected waves, and hence a useful analysis cannot be obtained. As a result, no concrete data on the sample can be generated. This in turn indicates that conventional ultrasonic micro spectrometers are subject to limitations in that the range of possible samples available for evaluation is restricted.